MARS, Pa. - Miles away from his defeat in Wisconsin, Rick Santorum rallied a crowd in his home state telling them he came to "kick off the second half" in southwestern Pennsylvania.

"We have now reached the point where its half time. Half the delegates in this process have been selected. And who is ready to charge down the field of Pennsylvania for a strong second half?" Santorum asked the crowd gathered in a ballroom at the Four Points Sheraton here.

"Pennsylvania and half the other people in this country have yet to be heard and we're going to go out and campaign here and across this nation to make sure their voices are heard," Santorum later added.

Earlier in the week, Santorum admitted for the first time that Pennsylvania's primary on April 24th is a must-win for his campaign. Over the next three weeks, Santorum plans to campaign heavily in the state, which Santorum said gained the nickname the "Keystone State" for a reason.

"We're the place upon which our country was built and great things continue to happen here," Santorum said.

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Santorum stressed the need to nominate a candidate who can present a contrast to Obama, saying "If we're going to win this race we can't have little differences between our nominee and president Obama. We have to have clear contrasting colors."

Without naming Romney by name, Santorum continued to hammer away at the Republican frontrunner, establishing himself as a candidate whose convictions are made of steel while Romney's are of the " etch-a-sketch" variety.

Looking beyond Pennsylvania, Santorum said he has "every intention" of winning in Texas, a state the campaign believes will be just as crucial to paving a way forward to the nomination as Pennsylvania.

"Pennsylvania's pivotal to our campaign, but it's pivotal to Romney's as well," Hogan Gidley, national communications director for Santorum, told reporters. "If we head into May with that win, then we have momentum going into the states that swing back our direction, and that's his worst nightmare because he wanted this thing to be over a long time ago, and it hasn't worked out that way, and so, you know, we think Pennsylvania and Texas are going to be pivotal to this nominating process

"I ask you over the next three weeks. This isn't half time. No marching bands. We are hitting the field. The clock starts tonight. We have three weeks to go out in Pennsylvania and win this state. And after winning this state, the field looks different in May," Santorum said.